Electrostatically sprayed polyamide powder coating
By preparing a novel polyamide resin containing a large number of terminal hydroxyl groups and cryogenically pulverizing it, the problem of low powder coating rate of polyamide powder coating in electrostatic spraying was solved, and the efficiency of single-pass coating thickness and production efficiency was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WANHUA CHEM GRP CO LTD
- Filing Date
- 2023-01-04
- Publication Date
- 2026-05-19
AI Technical Summary
Ordinary polyamide powder coatings have a low powder application rate during electrostatic spraying, resulting in insufficient coating thickness in a single spraying, which affects production efficiency and increases costs.
A novel polyamide resin containing a large number of terminal hydroxyl groups was used to prepare polyamide powder through cryogenic pulverization, thereby improving its polarization ability in the electrostatic spraying process, enhancing the powder application rate and the thickness of the coating in a single spraying.
It improves the powder application rate and the thickness of a single spray coating of polyamide powder coating, reaching more than 150 micrometers, thereby increasing production efficiency and reducing powder recovery and loss.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of powder coatings, and specifically relates to an electrostatic spraying polyamide powder coating. Background Technology
[0002] As people become increasingly aware of environmental protection, national laws and regulations are imposing stricter requirements, leading to restrictions on some coating processes that require organic solvents. To minimize environmental pollution, higher demands are being placed on coatings and coating processes. Powder coatings, compared to traditional solvent-based coatings, are more economical and environmentally friendly. In recent years, with the continuous development of new powder coating products and technologies, they have seen widespread application in numerous fields. Polyamide powder coatings, in particular, are increasingly widely used due to their chemical resistance, recyclability, and flexible processing.
[0003] Electrostatic spraying is a coating method that uses a high-voltage electrostatic field to cause negatively charged paint particles to move in the opposite direction of the electric field, thus adsorbing the paint particles onto the surface of the workpiece. Electrostatic spraying is relatively flexible and has low requirements for the shape of the parts, therefore it is widely used in various fields.
[0004] Because ordinary polyamide resins are not easily polarized, electrostatic spraying of polyamide powder often results in low powder application rates and small single-coat thicknesses. The thickness of a single electrostatic spray coating of ordinary polyamide powder is typically 90-130 micrometers. In some fields with specific coating thickness requirements, secondary spraying is necessary, significantly reducing production efficiency, increasing powder recovery and loss, and raising costs. Summary of the Invention
[0005] This invention prepares a novel polyamide resin containing a large number of terminal hydroxyl groups, which is easily polarized during electrostatic spraying, effectively improving the powder coating rate and the thickness of a single spray coating, thereby increasing production efficiency.
[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:
[0007] A polyamide powder coating for electrostatic spraying, the powder coating being obtained by cryogenic pulverization of a polyamide resin having the following structure:
[0008]
[0009] Wherein, R1 is a C1-C6 alkyl group, preferably one or more of -CH2-, -CH2-CH2-, and -CH2-CH2-CH2-, and R2 is a C1-C6 alkyl group, preferably... One or more of -CH2-CH2-, p / (p+y) is 0.02-0.2, preferably 0.04-0.14, and p and y are integers.
[0010] The aforementioned novel polyamide molecules contain a large number of terminal hydroxyl groups, which are easily polarized during electrostatic spraying, effectively improving the powder coating rate and the thickness of a single spray coating, thereby increasing production efficiency.
[0011] Another object of the present invention is to provide a method for preparing polyamide powder.
[0012] A method for preparing the above-mentioned polyamide powder, the method comprising the following steps:
[0013] S1: Polymer b is obtained by polymerizing olefin monomers containing amino groups;
[0014] S2: The hydroxy acid-terminated polyamide is polycondensed with polymer b to obtain polymer c;
[0015] Optionally, S3: Polyamide powder is obtained by pulverizing polymer c.
[0016] In this invention, the amino-containing olefin compound monomer in S1 is one or more of allylamine, 3-butenylamine, and 4-pentenylamine, preferably allylamine.
[0017] In this invention, the polymerization described in S1 is carried out under anaerobic conditions.
[0018] In this invention, the molecular weight of polymer b in S2 is 20,000-120,000, preferably 40,000-100,000.
[0019] In this invention, the polyamide in the hydroxy acid-terminated polyamide described in S2 is one or more of PA6, PA66, PA612, PA610, PA1010, PA1012, PA11, PA12, and PA1212, preferably one or more of PA6, PA11, and PA12.
[0020] In this invention, the hydroxy acid in the hydroxy acid-terminated polyamide described in S2 is hydroxybenzoic acid, lactic acid, or β-hydroxypropionic acid, with lactic acid being preferred.
[0021] In this invention, the number average molecular weight of the hydroxy acid-terminated polyamide in S2 is 200-5000, preferably 500-2000.
[0022] In this invention, the polycondensation described in S2 is carried out under anaerobic conditions.
[0023] In this invention, the pulverization process described in S3 is cryogenic pulverization followed by sieving.
[0024] In this invention, the polyamide powder particle size D50 of S3 is 40-80 micrometers, preferably 50-70 micrometers.
[0025] Another object of the present invention is to provide a polyamide powder.
[0026] A polyamide powder, wherein the polyamide powder is the polyamide powder contained in the above-mentioned polyamide powder coating, or is the polyamide powder prepared by the above-mentioned preparation method, and the polyamide powder has the following structure:
[0027]
[0028] Wherein, R1 is a C1-C6 alkyl group, preferably one or more of -CH2-, -CH2-CH2-, and -CH2-CH2-CH2-, and R2 is a C1-C6 alkyl group, preferably... One or more of -CH2-CH2-, p / (p+y) is 0.02-0.2, preferably 0.04-0.14, and p and y are integers.
[0029] Another object of the present invention is to provide a use for a polyamide powder coating.
[0030] An application of a polyamide powder coating, wherein the polyamide powder coating is the above-mentioned polyamide powder coating, or contains polyamide powder prepared by the above preparation method, or contains the above-mentioned polyamide powder, and the polyamide powder coating is used for electrostatic spraying, preferably for electrostatic spraying with a single spray coating thickness greater than 150 micrometers.
[0031] In one embodiment, using allylamine as the amino-containing olefin monomer, and taking lactic acid-terminated polyamide as an example, the preparation process of polyamide resin a is as follows:
[0032]
[0033] Compared with the prior art, the positive effects of the present invention are as follows:
[0034] (1) The polyamide powder coating has excellent powder application rate.
[0035] (2) Through electrostatic spraying process, the coating thickness formed by a single spraying can reach more than 150 micrometers. Detailed Implementation
[0036] The raw materials used in the examples and comparative examples are as follows:
[0037]
[0038]
[0039] The test equipment used in the examples and comparative examples is as follows:
[0040]
[0041] Example 1
[0042] 1) 2 mol of allylamine was dispersed in 5000 ml of a mixed solvent (methanol and water volume ratio 1:1). 0.2 mol of PVP K60 and 0.01 mol of AIBN were added sequentially to the system. The mixture was reacted at 50 °C under nitrogen atmosphere for 20 h. After dehydration and drying, polymer b was obtained. GPC analysis showed that polymer b had a number-average molecular weight of 40,000.
[0043] 2) 10 mol dodecyl lactam and 5 mol lactic acid were dispersed in ethanol. Under nitrogen protection, the temperature was gradually increased to 260℃ and the system pressure reached 1.5 MPa(G). The pressure was maintained for 1 h, and the gas was slowly released to atmospheric pressure. At the same time, the temperature was increased to 200℃ and the reaction was carried out for 0.5 h. The system was then kept at a constant temperature and evacuated for 0.5 h. After the reaction was completed, the nitrogen was released from the vacuum and the pressure was increased to 0.5 MPa(G) to obtain lactic acid-terminated polyamide. The molecular weight was 500 according to GPC test.
[0044] 3) 5 mol of lactic acid-terminated polyamide was dispersed in 5000 mL of ethanol and reacted with 0.05 mol of polymer b at 150 °C under a nitrogen atmosphere for 5 h. After cooling to room temperature, the mixture was filtered to obtain polyamide resin a. Infrared spectroscopy showed that polyamide resin a exhibited a fluorescence intensity of 3329 cm⁻¹. -1 A characteristic -OH peak appears.
[0045] 4) Polyamide resin particles were cooled and crushed using liquid nitrogen to obtain polyamide powder. The powder was then sieved using a powder sieving device, and the D50 value was measured to be 70 micrometers using a laser particle size analyzer. The polyamide powder was then sprayed onto a sample using an electrostatic spray gun. The sample was cured in an oven at 200°C for 5 minutes. After cooling, the coating thickness was measured to be 167 micrometers.
[0046] Example 2
[0047] 1) 2 mol of allylamine was dispersed in 5000 ml of a mixed solvent (methanol and water volume ratio 1:1). 0.2 mol of PVP K60 and 0.01 mol of AIBN were added sequentially to the system. The mixture was reacted at 50 °C under nitrogen atmosphere for 30 h. After dehydration and drying, polymer b was obtained. GPC testing showed that polymer b had a molecular weight of 80,000.
[0048] 2) 10 mol dodecyl lactam and 2.5 mol lactic acid were dispersed in ethanol. Under nitrogen protection, the temperature was gradually increased to 260℃ and the system pressure reached 1.5 MPa(G). The pressure was maintained for 1 hour, and the gas was slowly released to atmospheric pressure. At the same time, the temperature was increased to 210℃ and the reaction was carried out for 1 hour. The system was then kept at a constant temperature and evacuated for 1 hour. After the reaction was completed, the nitrogen was released from the vacuum and the pressure was increased to 0.5 MPa(G) to obtain lactic acid-terminated polyamide. The molecular weight was 1000 according to GPC test.
[0049] 3) 5 mol of lactic acid-terminated polyamide was dispersed in 5000 mL of ethanol and reacted with 0.1 mol of polymer b at 150 °C under a nitrogen atmosphere for 5 h. After cooling to room temperature, the mixture was filtered to obtain polyamide resin a. Infrared spectroscopy showed that polyamide resin a exhibited a fluorescence intensity of 3329 cm⁻¹. -1 A characteristic -OH peak appears.
[0050] 4) Polyamide resin particles were cooled and crushed using liquid nitrogen to obtain polyamide powder. The powder was then sieved using a powder sieving device, and the particle size distribution (D50) was measured to be 60 micrometers using a laser particle size analyzer. The polyamide powder was then sprayed onto a sample using an electrostatic spray gun. The sample was cured in an oven at 200°C for 5 minutes. After cooling, the coating thickness was measured to be 156 micrometers.
[0051] Example 3
[0052] 1) 2 mol of allylamine was dispersed in 5000 ml of a 1:1 mixture of methanol and water. 0.2 mol of PVP K60 and 0.01 mol of AIBN were added sequentially to the system. The mixture was reacted at 60 °C under nitrogen atmosphere for 38 h. After dehydration and drying, polymer b was obtained. GPC analysis showed that polymer b had a molecular weight of 100,000.
[0053] 2) 10 mol hexamethylenetetramine and 0.6 mol lactic acid were dispersed in ethanol. Under nitrogen protection, the temperature was gradually increased to 280℃ and the system pressure reached 1.5 MPa. The pressure was maintained for 1 h, and the gas was slowly released to atmospheric pressure. At the same time, the temperature was increased to 240℃ and the reaction was carried out for 2 h. The system was kept at a constant temperature and evacuated for 1.5 h. After the reaction was completed, the nitrogen was released from the vacuum and the pressure was increased to 0.5 MPa to obtain lactic acid-terminated polyamide. The molecular weight was 2000 according to GPC test.
[0054] 3) 5 mol of lactic acid-terminated polyamide was dispersed in 5000 mL of ethanol and reacted with 0.05 mol of polymer b at 150 °C under a nitrogen atmosphere for 5 h. After cooling to room temperature, the mixture was filtered to obtain polyamide resin a. Infrared spectroscopy showed that polyamide resin a exhibited a fluorescence intensity of 3329 cm⁻¹. -1 A characteristic -OH peak appears.
[0055] 4) Polyamide resin particles were cooled and crushed using liquid nitrogen to obtain polyamide powder. The powder was then sieved using a powder sieving device, and the particle size distribution (D50) was measured to be 50 micrometers using a laser particle size analyzer. The polyamide powder was then sprayed onto a sample using an electrostatic spray gun. The sample was cured in an oven at 200°C for 5 minutes. After cooling, the coating thickness was measured to be 153 micrometers.
[0056] Comparative Example 1
[0057] 10 mol of dodecyl lactam and 2.5 mol of lactic acid were dispersed in ethanol. Under nitrogen protection, the temperature was gradually increased to 260°C, and the system pressure reached 1.5 MPa(G). The pressure was maintained for 1 hour, and the gas was slowly released to atmospheric pressure while the temperature was increased to 210°C. The reaction was carried out for 1 hour under constant temperature and vacuum. After the reaction was completed, the nitrogen was released and the pressure was increased to 0.5 MPa(G) to obtain lactic acid-terminated polyamide. The molecular weight was 1000 according to GPC testing. The lactic acid-terminated polyamide particles were cooled and crushed by liquid nitrogen to obtain polyamide powder. The polyamide powder was obtained by sieving with a powder sieving device and the D50 was measured to be 60 micrometers by a laser particle size analyzer. The above polyamide powder was sprayed onto a sample using an electrostatic spray gun. The sample was cured in an oven at 200°C for 5 minutes. After cooling, the coating thickness was measured to be 113 micrometers. Compared with Example 2, the coating thickness was significantly reduced.
Claims
1. A polyamide powder coating for electrostatic spraying, characterized in that, The powder coating is obtained from a polyamide powder obtained by cryogenic pulverization of a polyamide resin, the polyamide having the following structure: Wherein, R1 is a C1-C6 alkyl group, R2 is a C1-C6 alkyl group, p / (p+y) is 0.02-0.2, and p and y are integers.
2. The polyamide powder coating according to claim 1, characterized in that, In the polyamide structure, R1 is one or more of -CH2-, -CH2-CH2-, and -CH2-CH2-CH2-, and R2 is... One or more of -CH2-CH2-, p / (p+y) is 0.04-0.14, and p and y are integers.
3. A method for preparing polyamide powder contained in the polyamide powder coating of claim 1, characterized in that, The method includes the following steps: S1: Polymer b is obtained by polymerizing olefin monomers containing amino groups; S2: The hydroxy acid-terminated polyamide is polycondensed with polymer b to obtain polymer c; S3: Polyamide powder is obtained by pulverizing polymer c.
4. The preparation method according to claim 3, characterized in that, The amino-containing olefin monomer in S1 is one or more of allylamine, 3-butenylamine, and 4-pentenylamine; And / or, the polymerization described in S1 is carried out under anaerobic conditions.
5. The preparation method according to claim 3, characterized in that, The amino-containing olefin monomer in S1 is allylamine.
6. The preparation method according to claim 3, characterized in that, The molecular weight of polymer b in S2 is 20,000-120,000; The polyamide in the hydroxy acid-terminated polyamide of S2 is one or more of PA6, PA66, PA612, PA610, PA1010, PA1012, PA11, PA12, and PA1212. And / or, the hydroxy acid in the hydroxy acid-terminated polyamide of S2 is lactic acid or β-hydroxypropionic acid; And / or, the number average molecular weight of the hydroxy acid-terminated polyamide described in S2 is 200-5000; And / or, the polycondensation described in S2 is carried out under anaerobic conditions.
7. The preparation method according to claim 6, characterized in that, The molecular weight of polymer b in S2 is 40,000-100,000; The polyamide in the hydroxy acid-terminated polyamide of S2 is one or more of PA6, PA11, and PA12; And / or, the hydroxy acid in the hydroxy acid-terminated polyamide of S2 is lactic acid; And / or, the number average molecular weight of the hydroxy acid-terminated polyamide described in S2 is 500-2000.
8. The preparation method according to claim 3, characterized in that, The pulverization process described in S3 is cryogenic pulverization followed by sieving. And / or, the polyamide powder of S3 has a particle size D50 of 40-80 micrometers.
9. The preparation method according to claim 8, characterized in that, The polyamide powder in S3 has a particle size D50 of 50-70 micrometers.
10. A polyamide powder, wherein the polyamide powder is the polyamide powder contained in the polyamide powder coating of claim 1 or 2, or is the polyamide powder prepared by the preparation method of any one of claims 3-9, characterized in that, The polyamide powder has the following structure: Wherein, R1 is a C1-C6 alkyl group, R2 is a C1-C6 alkyl group, p / (p+y) is 0.02-0.2, and p and y are integers.
11. The polyamide powder according to claim 10, characterized in that, In the polyamide structure, R1 is one or more of -CH2-, -CH2-CH2-, and -CH2-CH2-CH2-, and R2 is... One or more of -CH2-CH2-, p / (p+y) is 0.04-0.14, and p and y are integers.
12. Use of a polyamide powder coating, wherein the polyamide powder coating is the polyamide powder coating of claim 1 or 2, or contains polyamide powder prepared by any one of claims 3-9, or contains polyamide powder of claim 10 or 11, characterized in that, The polyamide powder coating is used for electrostatic spraying.
13. The use according to claim 12, characterized in that, The polyamide powder coating is used for electrostatic spraying with a single spray coating thickness greater than 150 micrometers.